1}2 HOLLAND: CHARNOCKITE SERIES. 



hypersthene-bearing rocks derived from more than one magma, 

 though all of very great antiquity. That, however, is a difficulty 

 which the stratigraphist has to face also in attempting to compare 

 the chronological values of different " epochs." Still, as long as we 

 keep in view several points of similarity between isolated exposures 

 of the charnockite series, the danger of including too much is parti- 

 ally insured against. As a set-off against this danger, there is a 

 strong probability that the magmas tapped in earlier geological 

 periods were larger than those which gave rise to eruptions after 

 the earth's crust had advanced in physical differentiation. 



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